A motor is widely used as a drive source for driving a pump. Recently, an inverter-integrated pump motor, in which an inverter is mounted to a motor, is becoming mainstream. The inverter has a power switching element (e.g., Insulated Gate Bipolar Transistor (IGBT), power MOS FET, or the like). With use of such a power switching element, the inverter can change input power of the motor and can thus operate the motor at variable speeds.
During driving of such pump motor, the inverter and the motor generate heat. In particular, the power switching element of the inverter generates high heat while it has a small surface area. As a result, the inverter is heated to have a high temperature. Various solutions have been conventionally proposed for cooling the inverter. For example, as shown in FIGS. 1A and 1B, there has been known a construction in which the inverter is cooled by a cooling fan for cooling the motor.
In the example shown in FIGS. 1A and 1B, a cooling fan 108 is mounted to a rotational shaft 103 of a motor 101 for driving a pump. A circular guide cover 110 is provided on the motor 101 so as to cover the cooling fan 108. A gap is formed between the guide cover 110 and the motor 101. Therefore, gas flow, generated by rotation of the cooling fan 108, advances through the gap along an outer circumferential surface of the motor 101 to cool the motor 101, while a part of the gas flow cools the inverter 105. An axial flow fan or a diagonal flow fan is used as the cooling fan 108, because mounting of this type of fan is easy and its major purpose is to cool the motor 101.
However, in the conventional cooling structure shown in FIGS. 1A and 1B, there exist the following drawbacks. The inverter 105 is coupled to a side surface of the motor 101 through a support member 111. From a viewpoint of facilitating its coupling structure, this support member 111 is typically arranged on a center line connecting the motor 101 to the inverter 105 when viewed from above. The support member 111 arranged in such a position prevents the gas flow delivered from the cooling fan 108 as shown in FIG. 1C, and as a result a cooling efficiency of the inverter 105 is lowered. In particular, use of a larger inverter 105 necessitates use of a larger support member 111, which would greatly disturb the gas flow for cooling the inverter 105.
When the axial flow fan is used as the cooling fan 108, the inverter 105 may not be cooled sufficiently because of a low flow rate of gas. In particular, the inverter 105, when used to drive the motor 101 for driving a pump requiring a large shaft power, is necessarily large. The axial flow fan cannot produce the gas flow powerful enough to cool such large inverter 105. Furthermore, when the axial flow fan or the diagonal flow fan is used, the gas flow directly strikes the motor 101 firstly, and thereafter its secondary gas flow strikes the inverter 105. As a result, the cooling efficiency of the inverter 105 is lowered.